Cellulosic structure and method for making same



Patented Apr. 14, 1942 CELLULOSIC STRUCTURE AND METHOD FOR MAKING SAME Franklin Traviss Peters, Wilmington, Del., assignor to E. L du Pont de Nemours &.Company, Wilmington, Del., a corporation of Delaware No Drawing. Application May 9, 1939, Serial N0. 272,639

14 Claims.

This invention relates to cellulosic. structures, especially those of pellicular nature. More particularly, it relates to a method forproducing flexible and durable cellulosic pellicles by treating the same with softening agents, and the products resulting from such treatment.

In the manufacture of cellulosic pellicles of the type precipitated from aqueous alkaline cellulosic solutions, such as regenerated cellulose pellicles, including sheets or fi ms, p bands, continuous tubing, artificial straw and the like, it has long been customary to incorporate into the cellulosic pellicle a softening agent in order to maintain it in a flexible condition. Such cellulosic pellicles, when free from a softening agent, are known to be quite brittle, and while a softener-free pellicle may find certain uses, a softened and therefore flexible sheet or film is much more generally useful.- Heretofore, as softeners for regenerated cellulose, and similar water-sensitive cellulosic pellicles, the art. has applied such substances as ethylene glycol, propylene glycol, diethylene glycol, formamide, glycowl, and the like, but of these, by far the most important is glycerol which has hitherto known no equal as a softening agent of general utility for producing flexible, transparent, and durable water-sensitive cellulosic pellicles such as those of regenerated cellulose. Many attempts have been made to find a softener for water-sensitive cellulosic pellicles which will be as cheap as and which will have the generally useful softenin characteristics of glycerol. After continued use of previously discovered softening agents they were found to be deficient in some respect and therefore could not be generally substituted for glycerol as a softening agent for regenerated cellulose and like water-sensitive cellulosic pellicles.

Glycerol is obtained commercially primarily as 1 a by-product from the soap industry. As a byproduct, the quantity may be limited and hence glycerol is subject to market fluctuations of supply as well as price. Glycerol has been particu-* 'larly high-priced and difflcultly obtainable during periods of war when large quantities are used in the production of munitions. The glycols, mentioned above as useful cellulose softeners,

development of less expensive equivalents or means for reducing the consumption of expensive materials will mean a marked economy in production.

It is, therefore, an object of this invention to provide a new and useful method for producing softened water-sensitive cellulosic materials possessing desirable physical properties. It is a further object-of this invention to provide watersensitive cellulosic materials having a softening agent associated therewith; which softening agent will not interfere with any subsequent treatment of the cellulosic pellicles, such as the application of surface coatings, ink, coloring l5 matter, adhesives, or the like. It is a still further object of this invention to provide a rigid, flexible, transparent, durable cellulosic pellicle, such as a sheet, film, or tube of regenerated cellulose in which the softening agent consists in whole or in part of a water-soluble amide ester of the type set forth' below. Other objects of the invention will appear hereinafter.

By the term rigidity" or its equivalent as used herein is meant that property which is the opposite of limpness; in other words, rigidity in package sealed, whereupon the durability may are for the most part obtained by a relatively expensive process of synthesis. The glycols are 1 also relatively volatile and are therefore unsatisbe measured against a known standard by dropping the package under standard conditions and noting the resistance of the wrapper to breakage. The objects of this invention can be attained, in general, by treating a regenerated cellulose pellicle, or a like water-sensitive cellulosic pellicle, with a softening agent comprising a watersoluble amide ester of the following structure:

in which R1 designates a hydrogen or a beta hydroxyethyl radical, R: designates an acyl group of 1 to 4 carbon atoms, and R3 designates an acyl group of 1 to 4 carbon .atoms, or a carbamyl group. As specific examples of such compounds may be mentioned: N-formyl-N(beta- HaOHaOII N-formyl-beta-carbamyloxyethylamine of the formula HCO-NH-CHrCHzOCONHz N-acetyl-beta-aminoethyl acetate, and N-propionyl-beta-aminoethyl propionate. The excess softening agent is then removed from the pellicle and the pellicle so treated is dried.

in the manufacture of regenerated cellulose sheets or films, as for example-by the viscose process, the cellulosic dispersion is formed into a sheet or film by passing the same through suitable apparatus'into coagulating and/or regenerating baths fromwhich it is finally obtained in the form. of a continuous cellulosic sheet which is customarily, led, in a continuous manner through a series of washing operatlonm Just prior to the drying operation which is also usually continuous, coordinating with the sheet forming and purification operations, the film is passed through a bath coutaining a. softening agent in such concentration that after the excess liquid has been removed from the surface of the sheet by suitable squeeze rolls'andthe excess moisture removed by passage through the dryer, the final sheet can be wound up in a continuous fashion and will contain an appropriate predetermined amount of softening agent.

The commercially available dry regenerated cellulose film contains approximately i to 8% moisture. Depending upon the particular uses for which the product is destined, the softening agent in the sheet or film, usually glycerol, may vary from about 8 to 25%, based on the combined weight of the cellulose and softening agent in the sheet.

The total amount of softener in the film is controlled primarily by the total amount of softening agent in the treating bath; film thickness, rate of passage through the bath,'temperature of the bath etc., may also contribute thereto to a certain extent. The regenerated cellulose pellicle, when reaching the treating bath, is in a highly swollen and hydrated condition and usually the cellulose of the pellicle is associated with 300% ..purifying, bleaching and.

or more of water. This highly swollen and wet pellicle, usually referred to as the gel sheet, is'

impregnated with the treating bath. Because of the large amount of water associated with the cellulose, it is apparent that the removal of this water during the drying operation will concentrate the softening agent with respect to the cellulose content of the pellicle;

Thus it is that if a regenerated cellulose pellicle containing about 15% total softener is desired as a. final product, the concentration of softener in the treating bath will be adjusted to approximately one-third that value, or about 5%. This is true when the softening agents are, like glycerol and the improved agents of this invention, sub

stantially non-volatile and are not vaporizeddurin: the drying operation. It mixed softener is used, the components of which are appreciably volatile during the drying operation, then the softener concentration of the treating bath must be increased-sufilciently to com pensate for the loss thereof during the' drying step.

is obvious that if asoftened with the materials of this invention possess desirable properties which are not found in similar pellicles in which the sole fiexibilizing and softening agent is glycerol.

The following examples will illustrate the practice of the invention, but it is to be understood that they are in no way limitative of the principles of the invention:

Example I A sheet or film ofgel regenerated cellulose in which the final dry thickness will be about .0009", is immersed in or drawn through an aqueous bath containing N formyl N(beta hydroxy ethyl) -beta.-carbamyloxyethylamine in such concentration that the final dry product will contain about 6.3% moisture and 15% softener, in the film. The sheet or film is allowed to remain in contact with the bath until thoroughly impregnated, whereupon it is removed from the bath, the excess liquid drained off or removed by suitable squeeze rolls, blotters, or the like, when the film can be dried in the usual manner down to the final moisture content indicated above. When tested in. a relative humidity of about 35% at 24 0.. or even at relative humidities as low as 15% to 22% at ordinary temperatures, the durability of the film is found to be at least equal to that of a similar regenerated cellulose film softened with about 14% glycerol.

Example I! A sheet or continuous film of gel regenerated cellulose such that the final dry thickness will be about- .0012" is treated in the manner described in Example I, using, however, a treating bath having a composition capable of prbviding a final .film containing about 6.3% moisture, and 18% 1 N -formyl-beta-carbamyloxyethylamine.

In this case the final product will be equal to or better than a. similar regenerated cellulose sheet or film bearing 15% to 16% glycerol as softener, insofar as its physical properties are concerned, including transparency, flexibility, and durability under varying conditions.

Sheets or continuous films of gel regenerated cellulose are treated as described in Example I,

substituting, however, the following treatment bath for the aqueous N-formyl-N(beta-hydroxyethyl) -beta-carba.myloxyethylamine solution of Example I.

Example 111 l Percent by weight N-acetyl-beta-.aminoethyl acetate 5.0 Water Y 95.0

propionate I estersare found to give highly desirable results.

For instance, the following compositions may be Percent by weight w substituted for the treatment bath of Example I:

Example V Percent by weight N-acetyl-beta-aminoethyl acetate 2.75 N-propionyl-beta-aminoethyl .propionate-.. 2.75, Water 94.5

' Example VI l Percent by weight N-acetyl-beta-aminoethyl acetate 2.25 N -'formyl-N(beta-hydroxyethyl) -beta carbamyloxy-ethylamine 3.25 Water I 94.5

Sheets or films of gel regenerated cellulose treated with any of the baths described in Examples III to VI, inclusive, in accordance with the procedure outlined in Example I, will show physical characteristics substantially equal to those of a similar regenerated cellulose sheet treated with a softener bath containing glycerol (thatis, a final film containing about glycerol), especially in physical properties such as transparency, flexibility, rigidity, durability, and the like.

In addition, films of regenerated cellulose softened with the amide esters of the 'present invention are found to have surface characteristics of slipperiness and lack of tackiness or tendency to cake together, which, in general, are equal to or superior to those obtained by the use of glycerol as a softener.

The following two examples illustrate a method for softening regenerated cellulosefilm with a treating bathrof the following approximate composition:

Percent by weight N-acetyl-beta-aminoethyl acetate 2.25 5 Ethylene glycol I. 2.75 Water 95.0

In this bath the ratio of N-acetyl-beta-aminoethyl acetate to ethylene glycol is about 1 to 1.22. The film is treated as described in Example I and yields a final product containing about 6.3% moisture, 6.75% of N-acetyl-beta-aminoethyl acetate, 6.6% of ethylene glycol. The ratio of N-acetyl-beta-aminoethyl acetate to ethylene glycol in the dried film is thus about 1.02:1.0, the amount of ethylene glycol having been decreased by loss during the drying operation. The dried film is subsequently provided with a surface coating which may be of any type desired. Thus, for example, it may be provided with a moistureproofing coating which may conveniently contain a cellulose derivative, a plasticizer, a

glycerol in combination with an ester of the present invention.

Example VI] A sheet or continuous film of gel regenerated cellulose similar to that of Example I is treated in the manner described in Example I, using, however, a treating bath of thefollowing approximate composition:

- Percent by weight Glycerol 2.5 N-formy' -N (beta-hydroxyethyl) -beta carbamyloxyethylamine 3.5 Water- 94.0

Similarly, the following treating bath may be used:

Example VIII Percent by weight Glycerol n: -2 2.25 N-acetyl-beta-aminoethyl acetate 3.25 Water 94.5

eration Example IX A sheet or continuous film of I gel regenerated cellulose, such that the final dry thickness will resin or blending agent, and a moistureproofing agent such as a wax or wax-like material; The coating in this case serves the double purpose of providing a moistureproof product and preventing loss by evaporation of the relatively volatile ethylene glycol. Even when tested under such drastic conditions as described in Example I, the product is transparent, flexible, and more durable than a similar film softened with 14% glycerol alone. F

It has been observed that the softening'agents of this invention have a tendency to somewhat soften the cellulose derivative coating which may be applied to the surface of the sheet or film. It will be noted, however, such a slight softening is, to a certain extent, highly advantageous. When a film cont ins as a softener a material which has a slight softening action for the coating composition subsequently appliedto the surface of the film, it will be found that the coating composition is more firmly bound to the surface of the base material than when the impregnating agent of the base has no such effect upon the coating composition. Where the amount required to soften the film is found to be such as to soften the coating'composition to an undesirable extent, the admixture of certain other softening agents well known in the art and as represented by Examples VII to IX, inclusive.

be about .0009'.', is immersed in or passed through will be found desirable.

Furthermore, a coating composition which is so bonded to the surface of the base sheet shows much less tendency to loosen and to flake off when the coated product is subjected to water and to relatively high humidities over long periods 01' time.

It is obvious that in the above examples the concentration of total softening agent in the treating bath may be suitably varied according to the base being treated in order that the final product will have th appropriate amount of.

softener.

As a base, the invention contemplates the use of any water-sensitive cellulosic structure, particularly of pellicular nature such as a sheet or film, artificial straw, caps, bands, or continuous tubes, such-as may be obtained by the coagulation and/or regeneration from an aqueous cellulosic dispersion in accordance with the procedure customary o the art. Thus, the invention comprehends the use of regenerated cellulose pellicles such as may be obtained from the viscose or cuprammonium processes, as well as pellicles simplified' The softening agents .softening of regenerated cellulose pellicles such or films of regenerated cellulose it as those sheets which are suitable for use as wrapping tissue,

includes any of the other bases set forth above and that the invention is equally applicable thereto.

All of the examples given have been set forth in terms of a sheet or film of gel regenerated cellulose (gel regenerated cellulose being defined as a water-swollen regenerated cellulose which has never been dried-hence that product which is obtainedfrom the wet end ofthe castingma chine). Obviously, this is the more practical way of practicing the invention, since the softening agent is customarily incorporated into the sheet or film while the latter is in the gel state and during thenormal course of manufacture. Obviously, if one desires to impregnate anv already dried regenerated cellulose film with a softener of the character described, it is possible to rewet the dried film so as to render it highly swollen, whereupon it may be treated with treating baths similar to those described, but of composition suitable for obtaining the final product desired. In the same way, any of the sheets set forth'as equivalent to regenerated cellulose sheets can be substituted in the specific examples.

The invention has been described in part in terms of the use of glycerol in combination with the softeners of the presentinvention. It is to be understood that other similar known cellulose softeners may be substituted for the glycerol and among those may be mentioned ethylene glycol, diethylene glycol, triethylene glycol, formamide, carbamide and other substances known to the art as softeners for water-sensitive cellulose structures.

It is also to be understood that various mixtures of the newly described softening agents may be employed with single softeners of the prior art or with mixtures of the latter, depending uponthe type of final film desired and the purposes for which the film is to be used.

If a colored cellulosic pellicle is desired, it may be obtained in any of the ways commonly known in the art, including the passage of the sheet or film through a bath containing a suitable dyestuff. If desired, the dyestuff'may be added to to the bath used for introducing the softening agent. In the same way, after the film has been treated with the softening agent, it may be subjected to any of the customary after-treatments such as sizing or coating, or the like, which may b customarily given to cellulosic pellicles of the type described, in just the same manner that a glycerol softened regenerated cellulose film. for example, may be treated.

The instant invention ofiers numerous advantages over the prior art means of softening cellulosic pellicles of the type described. Since the softening agents of the present invention are liquids at ordinary temperatures, the control of concentrations used for treating baths is greatly are available I physical characteristics,

- being understood that the scope of the invention in highly purified condition and consequently improve the quality of the final product. They do not crystallize after incorporation in the sheet in the concentrations useful for softening. They can be obtained synthetically at a very low cost in comparison to the cost of known softeners and they are available in unlimited quantity independent of a by-product source.

The use of the newly particularly improved transparency, flexibility, durability, surface characteristics and the like. In addition, when films of regenerated cellulose containing these softening agents arecoated with compositions comprising cellulose derivatives, for example nitrocellulose, they are found to give a coated product which is highly resistant to the effect of water and of humid atmospheres, and one in which the coating composition adheres much more tenaciously than when glycerol and softening agents heretofore used are employed.

Since it is obvious that many changes and modifications can be made in the above-described details without departing from the nature and spirit of the invention, it is to be understood that the invention is not to be limited thereto except as set forth in the following claims.

I claim:

i. A flexible, durable, water-sensitive, water-insoluble cellulosic structure of the 'type precipitated from aqueous alkaline cellulosic solutions,

. said structure containing, as a softener therefor,

an amide esterhaving the structure Ra-O -C :Hi-N

4 in which R1 designates a member of the group consisting of hydrogen and beta-hydroxyethyl radicals, R2 designates an acyl group of l to 4 carbon atoms',-and R: designates a member of the group consisting of acyl group of l to 4 carbon atoms and carbamyl groups.

2. A flexible, durable, regenerated cellulose structure, said structure containing. as a softener therefor, an amide ester having the structure in which R1 designates a member of the group consisting of hydrogen and beta-hydroxyethyl radicals, R2 designates an acyl group of 1 to 4 carbon atoms, and R: designates a member of the group consisting of acyl groups of l to 4 carbon atoms and carbamyl groups.

3. A flexible, durable, water-sensitive, water insoluble cellulosic structure of the type precipitated from aqueous alkaline cellulosic solutions, said structure containing, as a softener therefor, N- formylbeta-carbamyloxyethylamine.

4. A flexible, durable, water-sensitive cellulosic structure, said structure containing, as a softener therefor, N-acetyl-beta-aminoethyl acetate.

5. Regenerated cellulose softened, with N- formyl N(beta hydroxyethyl) beta-carbamyloxyethylamine.

6. Regenerated cellulose softened with N- fcrmvl-beta-carbamyloxyethylamine.

7. Regenerated cellulose softened with N- acetyl-beta-aminoethyl acetate.

described softening agents results in a product having improved 8. Regenerated cellulose softened with 8% to 25% of material having the formula:

I? I H CH3-(CH2);-C-OCHzCHrN-C(CH2)zCHa in which a: is a member of the group consisting of 0, 1 and 2.

9. Regenerated cellulose softened with 8% to 25% of material having the formula:

in which a: is a member of the group consisting of 0, 1 and 2, and R1 is a member of the group consisting of H and CH2CH2OH.

10. Regenerated cellulose softened with 8% to 25% of material having the formula:

0 it NHz-(J-O-CH2CHz-NC(CH:),H

in which a: is a member of the group consisting of 0, 1 and 2.

11. Regenerated cellulose softened with 8% to 25% of material having the'formula;

CHzCHzOH softener therefor, N formyl-beta-carbamyloxyethylamine.

14. A flexible, durable, water-sensitive cellulosic structure, said structure containing, as a softener therefor, N-formyl-N(beta-hydroxyethyl) -b eta-carbamyloxyethylamine.'

FRANKLIN TRAVISS PETERS. 

